1. Field of the Invention
This invention relates generally to a filtering apparatus, and more specifically relates to a replacement filter cartridge assembly for filtering water in pools, whirlpool-type tubs and other aquatic environments.
2. Description of the Prior Art
A certain type of replacement filter cartridge assembly 102 is particularly used in hot tubs, spas and other whirlpool-type environments. The filter cartridge assembly, which is shown in FIG. 1 in exploded perspective and in FIG. 2 in cross-section, includes a bottom end cap 104 having a central opening 106 formed through the thickness thereof, a top end cap 108 having a handle 110 extending from the outer surface thereof, a perforated cylindrical core 112 extending axially between and bonded to the bottom end cap 104 and the top end cap 108, and a pleated filter medium 114 situated between the end caps 104, 108 and disposed circumferentially about the core 112. This structure provides the replacement filter cartridge assembly 102 with a generally cylindrical shape.
The central opening 106 formed in the bottom end cap 104 includes two diametrically opposed notches 116. The central opening 106 receives an adaptor 118 or “nipple”, which is used for removably attaching the filter cartridge assembly to the filtering apparatus. The adaptor 118 includes a threaded base 120 at one axial end thereof for screwing the adaptor into the filtering apparatus, a perforated cage 122 at the opposite axial end thereof which may prevent hair entrapment and for receiving and containing an ion exchange cartridge (ionizer) which may contain cations such as Ag+2, silver/copper (Cu+2), copper and the like, a flange 124 extending radially outwardly from the outer circumference thereof which contacts the outer surface of the bottom end cap 104 of the filter cartridge assembly, when the cartridge assembly is properly seated on the adaptor 118, in order to form a water tight seal therewith, and two diametrically opposed bayonet prongs 126 which extend radially outwardly from the outer circumference of the adaptor. The two prongs 126 are dimensioned to be received by the opposite notches 116 formed in the central opening 106 of the bottom end-cap 104.
The prongs 126 of the adaptor 118 and notches 116 of the central opening 106 of the bottom end cap 104 cooperate to define a bayonet-type locking structure. When installing the filter cartridge assembly 102 in the filtering apparatus, the user simply grasps the filter cartridge assembly by the handle 110 on the top end cap 108, senses by feel the alignment of the notches 116 in the bottom end cap with the prongs 126 of the adaptor (which is already mounted in place on the filtering apparatus) and rotates the filter cartridge to misalign the notched portions in the bottom end cap 104 with the adaptor prongs 126. This simple action locks the filter cartridge assembly 102 to the adaptor 118 until it is time to replace the cartridge with a clean one.
The aforementioned replacement filter cartridge assembly works well in most situations. However, under certain conditions, it has been found that the filter cartridge assembly 102 may inadvertently become dislodged from the adaptor 118 within the filtering apparatus.
The adaptor 118 is preferably made from a liner high density polypropylene, while the end caps 104, 108 of the filter cartridge assembly 102 are preferably formed from a linear low density polyurethane. High density polypropylene is used in forming the adaptor 118 because of the intricacies of the adaptor that must be shaped, in particular, the perforated cone-shaped cage 122 which may prevent hair entrapment in the filtering apparatus and which creates an internal cavity to receive an ionizer.
As stated previously, the end caps 104, 108 are more suitably made from a linear low density polyurethane in order to form a strong compression fitting with the component of the filtering apparatus on which it is seated, in this case, the adaptor or nipple 118. A problem occurs when the low density polyurethane filter cartridge end cap is used in a heated aquatic environment with the high density polypropylene adaptor. Spa water temperatures exceed 100° Fahrenheit (F.). The low density polyurethane filter end cap 104, 108 has a greater coefficient of expansion than that of the high density polypropylene adaptor 118. The filter cartridge end caps thus soften and expand to a greater degree than the adaptor in the highly heated spa water, causing the diameter of the central opening 106 in the bottom end cap 104 to enlarge. When the filter pump is turned off, suction on the filter cartridge 102 is released. The filter cartridge, now fitting loosely on the adaptor 118, is free to rotate to a point where the bayonet prongs 126 on the adaptor align with the bottom end cap notches 116, resulting in the filter cartridge 102 becoming disengaged from the adaptor 118 and floating free therefrom within the filtering apparatus.